Thin films or layers made of silicon oxide, such as silicon monoxide (SiO) or silicon dioxide (SiO2), are excellent in electric insulating properties and high in mechanical strength as well and, therefore, are used as optical films and protective films for various electronics parts, and barrier films for devices, among others. Further, they are transparent and excellent in gas barrier properties, so that they are utilized also as surface coatings of food packaging materials.
Such silicon oxide thin films are generally formed by the so-called vapor deposition technique, namely by heating a silicon oxide species, which is a material for film formation as well as a material for vapor deposition, for evaporation thereof and for allowing the same to deposit on a substrate. In heating silicon oxide, various techniques, such as resistance heating, high frequency induction heating, electron beam heating and laser heating, are employed. In recent years, electron beams and plasma are used as the heat source in many instances.
In forming films utilizing electron beam heating or plasma heating, it is necessary to mold or form silicon oxide into cylinders or prisms and pelletize them for obtaining materials for film formation to be irradiated with electron beams or plasma.
Currently, silicon dioxide thin films are in the mainstream among silicon oxide thin films. However, in some cases, silicon dioxide thin films are unsatisfactory in adhesion to substrates according to the compatibility therebetween. Therefore, silicon monoxide thin films are preferably used in such and other cases.
As for the material for forming silicon monoxide thin films, there are disclosures in Publications of Unexamined Japanese Patent Application No. 63-166965 and No. 63-310961. According to the disclosures in these publications, silicon monoxide thin films are allegedly formed by vapor deposition using a material for film formation which comprises metallic silicon and silicon dioxide.
However, the materials for film formation as disclosed in these publications are neither uniform in composition nor good in evaporation characteristics, hence they raise problems, namely unequal film thicknesses and/or compositions result, and the formation of good silicon monoxide thin films becomes difficult.